Angiopteris involuta L.J. Jiang & Z.R. He, sp. nov. (Figure 3)

Type:— Qushui Town, Jiangcheng Hani and Yi Autonomous County, Yunnan Province, China, tropical seasonal rainforest along stream, alt. 324 m, 10 May 2024, L.J. Jiang 240510 (Holotype: PYU JLJ-09-1591!; Isotype: HITBC 0133890!).

Diagnosis:— Differs from related species by the combination of characters: mature individuals generally less than 120 cm tall (vs. up to 150 cm in Angiopteris itoi and A. sugongii); rhizome ascending (vs. erect in A. itoi); petioles minutely tuberculate (vs. smooth in congeners); fertile pinnules involute (boat-shaped with upturned margins, exposing partial sori abaxially; vs. flat in others); sori long linear, of intermediate length (2–8 mm; vs. 2–4 mm in A. sparsisora and A. caudatiformis; 10–20 mm in A. bipinnata and A. itoi); and leaf margins finely serrate (vs. coarsely dentate in A. bipinnata). The morphological comparison between A. involuta and the other three most similar species is provided in Table 4.

Description:— Plants terrestrial, 60–120cm tall. Rhizome stout, ascending. Fronds clustered, once pinnate or bipinnate. Stipes 45–60 cm × 5–8 mm, terete, sparsely tuberculate, densely covered with brown filamentous hairs when young (caducous), Sparsely covered with black, narrowly lanceolate scales (ca. 0.5–1.2 × 0.1 cm), as the leaves age, the color of the Stipe scales gradually changes from black to brown. Lamina to 120 cm, 1–2-pinnate; rachis wingless. Pinnae 5–6 pairs, narrowly lanceolate, 16–22 × 18–23 cm; bipinnate subtriangular, 45–55 × 18–23 cm, with 4–8 pairs of oblong pinnules 5–14 × 1.5–3 cm (apical ones slightly larger), base broadly cuneate, asymmetrical, with 2–4 mm petiolules, margins serrate; Veins sparse, simple or forked, false veins absent; texture herbaceous, adaxially green, abaxially pale green when dry. Fertile pinnules with margins strongly revolute toward adaxial surface (boat-shaped), partially exposing abaxial sori. Sori long linear, 2–8 mm, of 7–30 sporangial pairs, 2–3 mm from margin; paraphyses inconspicuous. Spores brown, trilete; exospores with densely tuberculate-spinose ornamentation. The spore mature from May to June.

Additional specimens examined (paratypes):— Qushui Town, Jiangcheng Hani and Yi Autonomous County Yunnan, CHINA, tropical seasonal rainforest along stream, alt. 350 m, 26 May 2025, L.J. Jiang 250526 (PYU!).

Etymology:— The epithet involuta refers to its involute fertile pinnules. The Chinese name is suggested as ‘ 卷叶 Kfiüẍ (juan ye guan yin zuo lian)’.

Distribution and habitat:— Endemic to southern Yunnan (Jiangcheng County) and grows in tropical seasonal rainforest understory along streams (270–350 m).

Conservation status:— Critically Endangered (CR B2ab (iii)). Only five wilds adult individuals and four ex situ specimens (XTBG nursery) are known. The type locality has been converted to rubber plantations, highlighting the urgent need for further field surveys in adjacent areas to assess potential remaining populations.

Notes: Molecular data place Angiopteris involuta in a clade with the species of Archangiopteris (A. bipinnata, A. chingii, A. latipinna, and A. nodosipetiolata Ting Wang tris, H.F. Chen & Y.H. Yan (2024: 181)), while A. itoi, A. sparsisora, and A. sugongii form a separate lineage (Wang et al. 2024) (Figure 2).

Key s to the species with fertile fronds with both once pinnate and bipinnate laminae of Angiopteris in China and surrounding regions:

1. Sori short-linear, usually less than 5 mm long, marginal ...................................................................................................................2

- Sori long-linear, usually more than 5 mm long, medial .....................................................................................................................4

2. Rhizome ascending; sori ca. 3–4 mm long, positioned 3–4 mm from the pinna margin ............................................... A. sparsisora

- Rhizome erect; sori ca. 1 mm long, positioned 0.5–1 mm from the pinna margin ............................................................................3

3. Stipe smooth; pinnules lanceolate ............................................................................................................................. A. caudatiformis

- Stipe with transversely raised stripes; pinnules oblanceolate, apex abruptly acute with a short caudate tip.................... amamensis

4. Rhizome erect (Taiwan) .............................................................................................................................................................. A. itoi

- Rhizome ascending (Yunnan).............................................................................................................................................................5

5. Plants small, mature fronds usually <1 m; veins sparse, 5–6 per cm; leaf margins coarsely serrate,sori ca. 4 mm from margin ...... .......................................................................................................................................................................................... A. bipinnata

- Plants large, mature fronds> 1 m; veins dense, 8–10 per cm; leaf margins undulate or minutely serrate, sori ca. 1–2 mm from margin.................................................................................................................................................................................................6

6. Stipes smooth, petiole scales reddish brown; fertile pinnules flat; exospores with spiculose ornamentation .................. A. sugongii

- Stipes sparsely tuberculate, petiole scales black or dark brown; fertile pinnules with revolute margins (boat-shaped); exospores with densely tuberculate-spinose ornamentation................................................................................................................ A. involuta